The invention relates to an electric machine comprising a permanent-magnetic excitation part and an induction part equipped with permanent magnets, said parts being movable relative to each other and said machine being in particular an electric machine commutated by means of electronic components.
Such electric machines, which are known, can be envisaged most easily with the aid of the comparative picture of a mechanically or electronically commutated d.c. motor with permanent-magnetic excitation, although the machine according to the invention by no means has to completely or largely correspond to this comparative picture. Conventional machines of this type have an M-n-characteristic (M meaning torque and n meaning speed of rotation) which, at least from a specific rotational speed range, decreases in pronounced manner as the rotational speed increases. The main cause thereof is that, as the rotational speed increases, the electromotive force (e.m.f.) induced in the machine increases and, consequently, only a lower current can still be "pressed" into the machine against this e.m.f. The fundamental correlation outlined holds also for electronically commutated machines in which the electronic commutation indeed can be controlled such that the current flowing through the machine is held approx. at the same level until a specific rotational speed range is reached; however, above this rotational speed range the machine current then decreases rapidly.